Thin film transistors (TFTs) are widely used in e.g. liquid crystal display devices and organic EL display devices. In particular, TFTs using amorphous silicon for the active layer are currently in widespread use for large liquid crystal display devices. However, there is demand for practical application of a novel active layer adaptable to e.g. larger size, higher reliability, and higher mobility in the future.
For instance, JP 2004-103957 A (Kokai) discloses a TFT using In—Ga—Zn—O-based amorphous oxide. This oxide can be film-formed at low temperature, and is transparent in the visible range. Hence, it has the potential to realize a transparent TFT that can be formed on a plastic substrate. Furthermore, a mobility of approximately 10 times that of amorphous silicon has been achieved.
In a TFT using such an oxide, further improvement in mobility is desired.